The present invention relates to a valve operation control device for an internal combustion engine having a selective coupling mechanism for selecting one of plural opening/closing modes of an intake or exhaust valve dependent on the hydraulic pressure applied and, particularly, to such a device in which there is a control valve disposed between the selective coupling mechanism and a hydraulic pressure supply source for varying the hydraulic pressure, and a control means connected to the control valve for controlling operation of the control valve dependent upon operating conditions of the engine.
One conventional valve operation control device of the type described is known, for example from Japanese Laid-Open Patent Publication No. 61-19911. In such conventional valve operation control device, a selective coupling mechanism is selectively supplied with lower and higher hydraulic pressures. When the lower hydraulic pressure is supplied, the lift and the opening interval of the controlled intake or exhaust valve are made larger than when the higher hydraulic pressure is supplied. The lower hydraulic pressure is supplied to the selective coupling mechanism when the engine rotates in a low speed range. In practice, if the engine continuously rotates in a high speed range due to a certain failure without switching operation of the selective coupling mechanism being effected, then the valve operating system may malfunction and the output power of the engine is not increased.
In view of the aforementioned problem, it is a first object of the present invention to provide a valve operation control device of an internal combustion engine, which detects the presence of a malfunctioning condition that prevents a selective coupling mechanism to effect switching operation in response to a change in operating conditions of the engine.
A second object of the present invention is to provide a valve operation control device for an internal combustion engine, which, in addition to achievement of the first object, takes appropriate action to avoid the malfunctioning condition when it is detected.